This invention relates to production of continuous filaments of a thermoplastic material and more particularly to improvements for producing such filaments where production apparatus uses mechanical attenuation of filaments from streams of heated thermoplastic material. The invention is especially useful in producing continuous glass filaments and strands of these filaments.
Normally heated thermoplastic materials such as molten glass are drawn into continuous filaments from streams flowing from a feeder holding a body of the heated material. Usually apparatus attenuates the streams into individual continuous filaments and combines them into a bundle or strand under the influence of pulling forces exerted directly by a winder. The winder collects the strand into a wound package on a collection tube mounted on a driven rotatable collet. The winders commonly used can collect strands at linear strand speeds in the order of 10,000 to 15,000 feet per minute or more.
Like other processes the glass fiber forming process is preferably kept running under controlled conditions on a substantially continuous basis with a minimum of operator attention. Accordingly, filament breaks, a major cause of process interruptions, must be kept at a minimum to effect quality of output and economy of production.
Numerous attempts have been made in the prior art at reducing the number of filament breaks to assure a more continuous process. For example U.S. Pat. No. 2,908,036 introduced fin shields which effected control and optimization of viscosity and temperature of the glass exiting from the feeder orifices. Also winders have been modified for more constant and uniform attenuation forces. Even sizing applicators have been improved to reduce the tension imparted when liquid coatings are applied to the filaments.
As the linear speed of the newly formed filament increases, the air drag on the filament also increases. And the pulling forces exerted by the winder must correspondingly be increased. Tests have shown that at the higher forming speeds, the air drag may account for 40% of more of the total tension forces in the filaments. The air drag may form an important variable causing filament breaks and higher winder pulling power.
The prior art patents such as U.S. Pat. Nos. 3,150,946 and 3,697,241 have introduced means for supplying cooling air to the glass streams and filaments. But prior art apparatus is notably deficient in supplying of high speed complementary air flow to reduce tension forces in the fiber forming process.